The present invention relates generally to document feeders, document feed methods, and image capture or reading devices, and more particularly to an automatic document feeder (ADF) and automatic document feed method in which feed a sheet from a stack of papers one by one. The document feeder and document feed method of the present invention are suitable for use with an ADF for in an image scanner, a photocopier, a facsimile unit, and other image capture devices.
Document feeders for use with image capture devices are classified into manual document feeders (MDFs) that require user""s sheet-by-sheet placement of sheet to be captured on a specified table, and automatic document feeders that automatically feed in a sheet to be captured from one or more sheets which have been placed by a user on a specified table. Thus, whereas the MDFs that require a user to separate sheets to be captured into a single one, the ADFs need include separation/feed means for separating a sheet to be captured from a plurality of sheets, and feeding the same to an image capture device.
A conventional ADF 1, as shown in FIGS. 32 and 33, typically includes a pick roller 2, a separation roller 4, a separation belt 6, a torque limiter 8, a leaf spring 10, a separation pad 12, and a transmission type sensor 14. Hereupon, FIG. 32 is a schematic sectional view of principal part of the conventional ADF 1. FIG. 33 is a schematic front view of a separation belt unit 5 in the ADF 1.
The pick roller 2, generally referred to as a feed roller, a pull-in roller, a dispense roller, or the like, is driven by a driving device (not shown) to rotate in an arrow direction in the drawing. The pick roller 2 touches a top of stacked papers placed on a hopper (not shown), and feeds one or more sheets from the top between the separation roller 4 and the separation pad 12. The pick roller 2 is located above of the hopper in the width direction of and in the middle of the hopper, so that the pick roller 2 and the hopper may move relative to each other. The separation belt 6 and the separation pad 12 are disposed opposite to the separation roller 4, and separate sheets into a single sheet in cooperation with the separation roller 4 if the pick roller 2 carries a plurality of sheets.
The separation belt 6 is an endless belt that moves depending upon the separation roller 4, and looped over a pair of rollers 7a and 7b that are spaced in a sheet feed direction. A torque of a specified value is fixed by the torque limiter 8 and applied to the separation belt 6. A compression force (separation load) of the separation belt 6 is applied to the separation roller 4 through the leaf spring 10, and this force determines a frictional force (driving force), which the separation belt 6 receives from the sheet. Thus, the separation belt 6 does not rotate unless a driving force larger than a braking force determined by the set torque and a size (diameter) of the separation belt 6 is applied to the separation belt 6. Normally, the compression force and the torque are determined in such a manner: (1) that if one sheet is inserted between the separation roller 4 and the separation belt 6, the sheet is held and carried without slippage by the separation belt 6; and (2) that if two sheets are inserted between the separation roller 4 and the separation belt 6, one of the sheets in contact with the separation belt 6 is held and stopped by the separation belt 6 while only the other sheet at the side of the separation roller 4 is carried to the next stage. The separation belt 6 and the torque limiter 8 are integrated to form a replaceable separation belt unit 5.
The transmission type sensor 14 detects a sheet at a downstream of the separation roller 4 and the separation belt 6. An output of the transmission type sensor 14 is connected with a timer means such as a counter (not shown) and a controller, whereby the controller may work out a sheet travel time using the timer means and an output from the transmission type sensor as a trigger. As a result, if a current sheet travel time is longer than a reference value, the controller determines that the sheet (i.e., sheet travel time) is longer than usual, assuming, for example, that two or more partially overlapped sheets are being carried.
However, the conventional ADF has several disadvantages. First, the conventional ADF cannot separate sheets stably (or cannot pick up only one sheet reliably). This is contrary to a recent demand on ADFs for quick feeding of various types of sheets with distinctive properties. In addition, even the same type of sheets may differ in separating condition according to temperature and humidity. An excessively low torque would cause double feeding, then resulting in jamming and poor-quality capturing, or the like. An excessively high torque would not feed any sheet, thereby slipping and jamming sheets on the separation belt 6. Worse yet, a user cannot easily adjust such an improper torque. For example, some experience is required to adjust the torque by the torque limiter 8 and the pressing force by the leaf spring 10. An inappropriate adjustment would make unstable the separation belt unit 5 and other neighboring members, causing a vibration associated with a feed action, and thereby rendering unstable the sheet separating action.
In addition, the conventional ADF 1 has no means for easily identifying a cause of unsuccessful sheet separation. For example, the ADF 1 has no means for checking whether the exchangeable separation belt unit 5 is properly installed. An improperly installed or uninstalled separation belt unit 5 would sometimes enable the ADF 1 to separate and feed a highly rigid sheet (e.g., cardboard) by virtue of the separation roller 2 and the separation pad 12. However, an unsuccessful sheet separation occurs when a user uses a low rigid sheet such as a thin sheet of paper in this condition. Thus, the user cannot easily ascribe the unsuccessful sheet separation to an improperly installed or uninstalled separation belt unit 5. Similarly, the conventional ADF 1 has no means for checking whether the separation belt 6 is worn out, and thus a user cannot easily ascribe the unsuccessful sheet separation to the worn separation belt 6.
Still disadvantageously, the conventional ADF 1 cannot detect double feeding reliably using the transmission type sensor 14. because an output of the transmission type sensor 14 varies with sheet""s property (such as color, thickness, type, material. and the like). In other words, the transmission type sensor 14 typically uses light-emitting and light-sensitive elements, but they do not exhibit such a high performance as to detect the double sheet feeding with transmittance. In particular, the transmission type sensor 14 can hardly detect the double feeding where different types of sheets are being fed.
Moreover, the separation belt 6 and the torque limiter 8 are both consumable in the separation belt unit 5, and the replacement of the unit costs much.
Accordingly, it is a general and exemplified object of the present invention to provide a novel and useful document feeder, document feed method, and image capture device, in which the above disadvantages are eliminated.
Another exemplified and more specific object of the present invention is to provide a document feeder, document feed method, and image capture device that deliver high performance in sheet separation.
Another exemplified object of the present invention is to provide a document feeder, document feed method, and image capture device that serve to identify a failed component in a sheet separation mechanism.
Another exemplified object of the present invention is to provide a document feeder, document feed method, and image capture device that can reliably detect the double sheet feeding.
In order to achieve the above objects, a document feeder as one aspect of the present invention includes a pull-in portion that contacts a topmost sheet among a plurality of sheets and feeds one or more sheets including the topmost sheet, and a sheet separation mechanism that restricts the number of sheets to be fed by the pull-in portion. The sheet separation mechanism includes a first separation portion that contacts the sheet, and moves so as to feed the sheet, a second separation portion, located opposite to the first separation portion, which defines a part of a sheet feed path between the second and first separation portions, and moves so as to allow the sheet to be fed, and a brake portion that variably applies to the second separation portion a load allowing the second separation portion to move. This document feeder can adjust a braking force (load) properly according to various types of sheets.
A document feed method as another aspect of the present invention includes the steps of sequentially pulling in stacked sheets from a top thereof, restricting using a sheet separation mechanism the number of sheets to be fed, the sheet separation mechanism including a first separation portion that contacts the sheet, a second separation portion, located opposite to the first separation portion, which defines a part of a sheet feed path between the second and first separation portions, and moves so as to allow the sheet to be fed, and applying variably to the second separation portion a load allowing the second separation portion to move. This document feed method can adjust a braking force (load) properly according to various types of sheets.
A document feed method as still another exemplified embodiment of the present invention includes the steps of sequentially pulling in stacked sheets from a top thereof, restricting using a sheet separation mechanism the number of sheets to be fed, the sheet separation mechanism including a first separation portion that contacts the sheet and move so as to feed the sheet along a sheet feed path, a second separation portion, located opposite to the first separation portion, which defines a part of the sheet feed path between the second and first separation portions, and moves so as to allow the sheet to be fed, detecting a moving condition of the second separation portion, determining whether a double feeding of the sheets has occurred, and measuring a feed time of the sheet, wherein the determining step determines that there is the double feeding of the sheets, when the measuring step measures that the feed time of the sheet is longer than a reference value, and the detecting step detects a motionless and improper movement of the second separation portion. This document feed method determines an existence of a double feeding by taking into account a moving condition of the second separation portion, and thus provides a higher reliability than a method of determining the double feeding only based on a measured sheet feed time period.
The image capture device as one embodiment of the present invention includes the above-described document feeder, and a reader part that reads out information on a sheet that is fed by the document feeder. This image capture device has the same effects as the above-described document feeder.
Other objects and further features of the present invention will become readily apparent from the following description of the embodiments with reference to accompanying drawings.